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United States Patent |
5,675,140
|
Kim
|
October 7, 1997
|
Autofocus control device with a light source
Abstract
An optical positioning device using astigmatic optical elements. A laser
diode emits astigmatic, elliptically shaped light which is not corrected.
A first lens condenses the light and transmits the light to an object to
be positioned. The light reflected off of the object is monitored while
the object is moved. Because of astigmatism, the first lens does not have
a true focal point. There is a point, however, where the vertical and
horizontal components of the transmitted light are equal. The first lens
is positioned so that the desired position of the object corresponds to
this equal point.
Inventors:
|
Kim; Sang-Cheol (Kyungki-do, KR)
|
Assignee:
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Samsung Aerospace Industries, Ltd. (Kyungsangnam-do, KR)
|
Appl. No.:
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598956 |
Filed:
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February 9, 1996 |
Foreign Application Priority Data
Current U.S. Class: |
250/201.2; 250/201.4; 355/55; 356/400 |
Intern'l Class: |
G02B 007/04; G02B 027/64 |
Field of Search: |
250/201.2,201.4,201.5,548
356/399,400,401
355/53,55
|
References Cited
U.S. Patent Documents
4687322 | Aug., 1987 | Tanimoto et al. | 355/55.
|
4701606 | Oct., 1987 | Tanimoto et al. | 250/201.
|
5286963 | Feb., 1994 | Torigoe | 250/201.
|
5483056 | Jan., 1996 | Imai | 250/201.
|
5489966 | Feb., 1996 | Kawashima et al. | 355/55.
|
Primary Examiner: Westin; Edward P.
Assistant Examiner: Pyo; Kevin
Attorney, Agent or Firm: Finnegan, Henderson, Farabow, Garrett & Dunner, L.L.P.
Claims
What is claimed is:
1. A device for positioning an object using astigmatic optical elements
without correcting astigmatism, the device comprising:
a light source for emitting light, the light having astigmatism and being
elliptical;
a first lens for condensing the elliptical light emitted from the light
source and for transmitting the light to the object;
a second lens for condensing light reflected off of the object;
a photodetector for receiving light from the second lens and converting the
received light into electrical signals; and
control means for receiving the electrical signals and for controlling the
position of the object in accordance with the electrical signals.
2. The device as claimed in claim 1, wherein the first and second lenses
are spherical lenses.
3. The device as claimed in claim 2, further comprising a first reflector
in the light path between the first lens and the object and a second
reflector in the light path between the object and the second lens.
4. The device as claimed in claim 2, wherein the photodetector comprises
four photodiodes.
5. The device as claimed in claim 3, wherein the control means comprises:
an amplifier circuit for receiving and adjusting the electrical signals;
an analog to digital converter for converting analog signals from the
amplifier circuit to digital signals;
a processor circuit for receiving the digital signals and for determining
the position of the object in accordance with the digital signals, the
processor circuit producing a control signal; and
means for moving the object in accordance with the control signal.
6. The device as claimed in claim 1, wherein the light source comprises
laser diode.
7. An optical disk player including the device claimed in claim 1.
8. A projection optical system for manufacturing semiconductor devices
including the device claimed in claim 1.
9. A device for positioning an object using astigmatic optical elements
without correcting astigmatism, the device comprising:
a light source for emitting light, the light having astigmatism and being
elliptical;
a first lens for condensing the elliptical light emitted from the light
source and for transmitting the light to the object;
a cylindrical lens in the light path between the light source and the
object;
a second lens for condensing light reflected off of the object;
a photodetector for receiving light from the second lens and for converting
the received light into electrical signals; and
control means for receiving the electrical signals and for controlling the
position of the object in accordance with the electrical signals.
10. The device as claimed in claim 9, wherein the first and second lenses
are spherical lenses.
11. The device as claimed in claim 10, further comprising a first reflector
in the light path between the first lens and the object and a second
reflector in the light path between the object and the second lens.
12. The device as claimed in claim 10, wherein the photodetector comprises
four photodiodes.
13. The device as claimed in claim 11, wherein the control means comprises:
an amplifier circuit for receiving and adjusting the electrical signals;
an analog to digital converter for converting analog signals from the
amplifier circuit to digital signals;
a processor circuit for receiving the digital signals and for determining
the position of the object in accordance with the digital signals, the
processor circuit producing a control signal; and
means for moving the object in accordance with the control signal.
14. The device as claimed in claim 9, wherein the light source is comprised
of laser diode.
15. An optical disk player including the device claimed in claim 9.
16. A projection optical system for manufacturing semiconductor devices
including the device claimed in claim 9.
17. A method of positioning an object at a desired position using
astigmatic optical elements without correcting astigmatism, the method
comprising the steps of:
providing an astigmatic beam of light, the astigmatic beam of light having
a horizontal component and a vertical component, and the astigmatic beam
of light having an equilibrium point at which the horizontal and vertical
components are equally out of focus;
transmitting the light to the object;
moving the object;
monitoring the light reflected off of the object; and
detecting the equilibrium point.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to an autofocus control device
using an elliptical light. In equipment for lithography-semiconductor
manufacturing and compact disk (CD) players, the present invention relates
to an autofocus control device using an elliptical light, that either
places a workpiece in the range of focus-depth of a projection lens or
places a compact disk at the focus plane of a reading beam.
(2) Description of the Prior Art
Light-exposure equipment for lithography-semiconductor manufacturing shifts
a geometrical-shaped pattern on a mask into a thin screen covered surface
of a semiconductor wafer. To shift the patterns on the mask, the wafer and
workpiece must be within the focus depth-of-field of a projection lens.
Information is recorded as pits in an optical disk, and a light source
reads the information. Lasers typically produce the reading beam light
source. According to an electric signal transmitted from the reflected
light, after reading the information, the reader places the disk at the
focal point of the laser beam.
In optical systems for semiconductor manufacturing and compact disk
players, an autofocus control device is used to place disk, wafer, and
workpiece in the exact focus plane.
In light-exposure and light pickup devices, the autofocus control uses
circular light. Laser diodes, however, emit astigmatic, elliptically
shaped light.
For example, a lens in the light-exposure equipment condenses circularly
shaped light on the wafer or workpiece. The light-exposure equipment then
condenses the reflected light onto a photodetector. At this time, any
change in position is detected, and the focus position of the wafer and
workpiece is also detected. The wafer and workpiece is then placed within
the focus depth of field.
An autofocus control device may use astigmatism. For example, in a compact
disk player, an elliptical light beam emitted from laser diode is
converted into a circular light beam, and astigmatism enables the disk to
be located on the focus plane. Thus, while camera lenses are designed to
reduce astigmatism, the light pickup device uses the largest possible
astigmatism to detect focus errors.
The autofocus control device using astigmatism converts emitted light into
circular-shaped light. A cylindrical lens then transmits the
circular-shaped light into elliptical-shaped light. A spherical lens
condenses the light at a workpiece. A four way divided quad detector
detects light reflected from the workpiece and detects the position of the
workpiece by the detected signal. In the above-mentioned manner, an
autofocus control device generates an astigmatism using the cylindrical
lens and the spherical lens.
SUMMARY OF THE INVENTION
The advantages and purpose of the invention will be set forth in part in
the description which follows, and in part will be obvious from the
description, or may be learned by practice of the invention. The
advantages and purpose of the invention will be realized and attained by
means of the elements and combinations particularly pointed out in the
appended claims.
An object of the present invention is to provide an automatic controller
using a simple laser diode.
A further object of the invention is to provide an automatic controller
which does not convert elliptical light into circular light, but rather
uses the elliptical light to automatically position an object.
Another object of the present invention is to provide an automatic
controller which places a workpiece, a wafer, and/or an optical disk
within the focus depth of a projection optical system.
To achieve the objects and purposes of the invention, the construction of
the invention is as follows. A light source emits oval light emitted from
the light source. A first reflector reflects the oval light from the 1st
spherical lens and transmits the light to an object to detect the
position.
A second reflector reflects the light reflected by the object to detect the
position. A second spherical lens condenses the light reflected from the
second reflector. A photodetector converts light from the second spherical
lens into corresponding electric signals and outputs the signals. A
control means reads position information of corresponding object to detect
the position according to the electric signal from the photodetector and
according to the read information, outputs a control signal. A position
adjusting part receives the control signal and adjusts the position of the
object.
The light source of the preferred embodiment of this invention is commonly
constructed by laser diode. This invention is not limited to the
embodiment described here and can be modified within the scope of the
invention.
It is to be understood that both the foregoing general description and the
following detailed description are exemplary and explanatory only and are
not restrictive of the invention, as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of this specification, illustrate several embodiments of the invention and
together with the description, serve to explain the principles of the
invention. In the drawings,
FIG. 1 is a perspective view of an autofocus control device according to a
first embodiment of the present invention;
FIG. 2 is a schematic diagram of a laser diode;
FIG. 3 is a schematic diagram illustrating the cross-sectional shape of
transmitted light beams according to the first embodiment of the
invention;
FIGS. 4A-4C are state-diagrams of the cross sections of light impinging on
a photodetector; and
FIG. 5 is a perspective view of an autofocus control device according to a
second embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to a preferred embodiment of the invention, an optical
positioning device uses astigmatic optical elements. A laser diode emits
astigmatic, elliptically shaped light which is not corrected. A first lens
condenses the light and transmits the light to an object to be positioned.
The light reflected off of the object is monitored while the object is
moved. Because of astigmatism, the first lens does not have a true focal
point. There is a point, however, where the vertical and horizontal
components of the transmitted light are equal. The first lens is
positioned so that the desired position of the object corresponds to this
equal point.
Referring to FIG. 1, the first embodiment of the present invention is a
projection optical semiconductor manufacturing device. A mask 1, has a
pattern to be projected. A projection lens 2 projects the light passing
through the mask 1. A workpiece 3 comprises a wafer and a workpiece to
shift the patterns on the mask.
A laser diode 4 emits oval light to detect the position of workpiece 3. A
first spherical lens S condenses the oval light emitted from laser diode
4. A first reflector 6 reflects the light condensed from the spherical
lens 5 to the workpiece 3. A second reflector 7 reflects the light
reflected by the first reflector 6 to the workpiece 3 again. A second
spherical lens 8 condenses the light reflected by the second reflector 7
and outputs the light. A photodetector 9 detects the light projected from
the second spherical lens 8 and outputs a corresponding electric signals.
An amplifier/gain controller 10 amplifies the electric signals from the
photodetector 9. An A/D converter 11 receives the amplified electric
signals and converts the analog signals into digital signals. A
controlling part 12 receives the digital signals and determines the
position of the workpiece 3. The controlling part 12 then outputs a
controlling signal to position the workpiece 3. A position adjusting means
13 controls the position of the workpiece 3 according to the controlling
signal from the controlling part 12.
The workpiece 3 resets on a non-drawn stage (not shown). The position
adjusting means 13 moves the non-drawn stage to place the stage in the
image-position.
The invention can be used as the light arranging means of light-exposure
equipment, to read the information on a disk.
A non-drawned laser power controller is used as arranging light source in
light-exposure equipment, and also, emits a regular shaped quantity of
light.
When a user operates the power device, a laser diode 4 emits light. The
light emitted from the laser diode 4, as shown in FIG. 2, has astigmatism
and an elliptical or oval-shape. The elliptical light from the laser diode
4 is condensed through first spherical lens 5 and transmitted to the
workpiece 3 by the reflector 6.
In this application, astigmatism refers to a difference in focus between
vertical and horizontal components of a light beam FIG. 3 illustrates the
cross-sectional areas of light emitted from the laser diode 4 and
condensed by the first spherical lens 5. As the light emitted from the
laser diode 4 comprises astigmatism, horizontal light is condensed at a;
vertical light is condensed at c; and the cross-sectional area is circular
at b.
Referring again to FIG. 3, as the horizontal light is focused at position a
and the vertical light is not, the light at a is oval-shaped. Because the
vertical axis is out of focus at position a, the vertical component of the
cross-sectional area is longer than the horizontal component.
The lens 5 focuses the vertical component of the light at position c, but
the horizontal component is out of focus at position c. Therefore, the
cross-section of the light is oval-shaped with a longer (out of focus)
horizontal axis.
At position b, both the horizontal and the vertical components of the light
are out of focus. However, the horizontal and vertical components are
equally out of focus at position b, and a circular cross-sectional area
results.
Reflector 6 reflects the light onto the workpiece 6. The lens 5 and the
reflector 6 are positioned so that the circular cross-sectional light, as
shown at position b in FIG. 3, will impinge on workpiece 3 if workpiece 3
is properly positioned.
In the preferred embodiment, the photodetector 9 has four photodiodes
arranged as shown in FIG. 4A. The photodetector, thus, divides the light
beams into four segments a-d and outputs corresponding electrical signals.
The signals from the photodetector 9 are adjusted into proper values by
amplify/gain controller 10 and converted by A/D (Analog/Digital) converter
11. According to the digital signals, the controlling part 12 adjusts the
wafer and workpiece, namely, the position of the stage which contains the
workpiece.
FIG. 4A shows the shape and position of light impinging on the
photodetector 9 corresponding to position a. FIG. 4B shows the shape and
position of light impinging on the photodetector 9 when workpiece 3 is
located exactly at the image point of the projection lens 2 corresponding
to position b. FIG. 4C shows the shape and position of light impinging on
the photodetector 9, when workpiece 3 is located inside of the image point
of projection lens 2 corresponding to position c.
The controlling part 12 determines the position of the workpiece 3 from the
signals a-d from the photodetector 9. The controlling part 12 calculates:
(a+b)-(c+d)=.alpha. (1)
(a+c)-(b+d)=.beta. (2)
The position adjusting means 13 moves the workpiece 3 to calculate a series
of .alpha.' s and .beta.' s. When .alpha. and .beta. are a minimum or
zero, the above controlling part 12 regards that workpiece 3 is located at
the image point of the projection lens 2. The controlling part 12 adjusts
the position of workpiece 3, according to the signals detected by the
photodetector 9. The workpiece 3 is preferably positioned at the focal
point of the projection lens 2 or at least within an acceptable depth of
field.
The position adjusting part 13 and controlling part 12 are adjustable.
The second embodiment of the invention is also an autofocus control device
using a laser diode. Referring to FIG. 5, the second embodiment includes a
cylindrical lens 14 between the laser diode 4 and the first spherical lens
5 to increase astigmatism.
The cylindrical lens 14 has an astigmatism in relation to circular light in
accordance with an embodiment of this invention. The position information
of workpiece 3 from photodetector 9 is obtained and the operating system
is similar to the first embodiment. However, the astigmatism of light
emitted from cylindrical lens 14 is increased and the intervals between
positions a, b, and c are extended. The photodetector 9, therefore,
conveniently obtains the position information.
Thus, the positioning device operates without converting the elliptical
light emitted from the laser diode into circular light. The workpiece of
light-exposure equipment or the disk of a CD player is located, in the
range of focus-depth or at the exact focus position. The present invention
differs from devices which combine a cylindrical lens and a spherical lens
again, and then makes an astigmatism, after forming the elliptical light
into the spherical light.
The present invention is designated to detect conveniently the position
information, and an autofocus control device using a laser diode that
reduces the expense of production and the occupied area.
Other embodiments of the invention will be apparent to those skilled in the
art from consideration of the specification and practice of the invention
disclosed herein. It is intended that the specification and examples be
considered as exemplary only, with the true scope and spirit of the
invention being indicated by the following claims.
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